1. Field of the Invention
In its broader aspects, the present invention relates generally to the field of strip handling and more particularly to apparatus for detecting a locator or locators associated with a strip even though the strip is subject to wavering movement as it is advanced through the apparatus. In a preferred species, the present invention pertains to a photographic printer that includes means for detecting a locator, e.g. a perforation, notch or mark, associated with each image frame of a film strip that is advanced through the printer, even though the strip is subject to wavering movement as it is advanced through the printer.
2. Description of the Prior Art
In the prior art it is known in the photo-finishing arts to receive strips of exposed photographic negative frames from various customers and to join like types of film, e.g. size 110 film, end-to-end to form one elongated film strip that may be conveyed first through a photographic film processor to develop the exposed frames and then through an automatic photographic film printer, such as the 2610 Color Printer manufactured by Eastman Kodak Company, Rochester, New York, to reproduce images on the negative frames onto positive photographic print material. The strips are then separated from each other and, after processing of the positive print material, returned to the customers with matching positive prints. In an automatic printer that includes both a negative frame scanning gate and a negative frame printing gate, the strip is removed from a supply spool and incrementally advanced through these gates towards a take-up spool. Each frame is serially located first within the scanning gate and then within the printing gate. The two gates are so located relative to one another as to permit simultaneous scanning of one frame and printing of another frame onto photographic print material that is incrementally moved through the printer in synchronism with the movement of the frames of the film strip. In the vicinity of the scanning gate, the printer includes suitable apparatus for scanning the negative frame in the gate. This is done to obtain information relative to the photographic exposure characteristics of the negative, which information is useful in making a print from the negative when the negative frame is subsequently moved to the printing gate.
A factor associated with the printing and scanning operations is alignment of the frames in the respective gates. If the film strip is comprised of either size 110 or size 126 negatives, each frame will have one perforation or sprocket hole that is associated with the frame. A pawl may be provided on the printer adjacent the scanning gate to detect a perforation by entering it and thereby locating the particular frame in proper position relative to the scanning gate. Suitable means may be provided for sensing the movement of the pawl into the perforation for stopping the drive to the film strip. Since a uniform pitch is provided between frames, another frame will be positioned in the printing gate.
If the film strip is comprised of size 135 negatives, each frame will have adjacent thereto a notch formed in one edge of the film strip. The notch serves as a locator or identifier for that frame and can be detected by a photoelectric pickup device. The device, upon detection of this notch, produces a signal that is delivered to a computerized control which determines the appropriate time to issue a signal to terminate a drive that is advancing the strip. The strip will then be stopped and the appropriate frame will be located in the scanning gate. Because the pitch between size 135 type negative frames is not always uniform, simultaneous scanning of one negative while another is being printed may be accomplished by having the film strip form a free loop between the scanning gate and the printing gate. This permits one frame to be precisely located in the scanning gate and another frame to be simultaneously precisely located in the printing gate.
As described above, the operation of locating a negative frame in the scanning gate assumes that a locator for each frame is detected by a detector such as a pawl or a photoelectric pickup device. To ensure the detection of these locators it has been the practice heretofore to constrain transverse movement of the strip adjacent the detector so that the locators cannot bypass the detector as the strip is advanced. The transverse constraint has been accomplished by providing two pins, one for each lateral edge of the strip, and fixing these pins a distance apart approximately equal to the nominal width of the film strip. The pins and detector are located adjacent the scanning gate so that the locator for each frame may be detected prior to the frame's being completely positioned within the scanning gate. The pins, because of their close proximity to the scanning gate, also serve to align the frame against transverse offset movement while the frame is in the scanning gate. A similar set of pins and another detector may be associated in a like manner with the printing gate.
A problem associated with printers of the kind described above arises from the fact that an elongated film strip formed by splicing together a plurality of very much shorter film strips is likely to have splices at which the meeting ends of the strips are not precisely aligned. When conveying the imprecisely formed elongated film strip and simultaneously imposing constraints against lateral movement, such as by pins at the scanning and printing gates, the elongated film strip tends to waver where it is not constrained. In the printer described above, wavering movement of a size 110 or size 126 film strip was allowed to occur where the film strip was supported on a drive roller that was located downstream of the printing gate. The drive roller was driven by a tendency drive arrangement; thus, some slip between the roller and strip was tolerable and the strip could be allowed to waver along the roller in an axial direction. In the case of a size 135 film strip, the free loop provided between the gates permitted the film strip to waver while being rigidly constrained at each of the two gates. The presence of the free loop, however, required an additional drive arrangement to drive the film strip from the scanning gate into the free loop.
In the case of a size 135 film strip it would be desirable to eliminate the need for a free loop since an extra motor is required to maintain the loop. Even though elimination of the free loop removes the possibility of precisely simultaneously locating out-of-pitch frames in both the scanning and printing gates, it has been found that precise location of a negative in the scanning gate is unnecessary. Thus, after precisely aligning a frame in the printing gate, suitable computer controlled means can be provided for determining if a sufficient portion of a negative is located in the scanning gate to provide a reasonably accurate assessment of the exposure characteristics of the negative. If a sufficient portion of the negative is so located then the negative can be scanned simultaneously with the printing of a negative in the printing gate. If a sufficient portion of the negative is not so located then the negative in the printing gate can be printed and the drive thereafter advanced to locate a sufficient portion of the negative in the scanning gate.
It would also be desirable when printing from size 110, size 126 and size 135 film strips to provide a positive drive, such as from a stepper motor, for feeding the strip through the gates. The use of a positive drive assures that no slip will occur between a drive roller that is positively driven and the film strip that it is driving, and thus permits accurate computer-controlled movement and stopping of the strip. In addition, the positive drive eliminates the need for an additional motor for pulling a strip from the supply spool as was required for the tendency drive arrangement described above. Furthermore, it eliminates the need for a pawl to stop the strip as the strip is immediately stopped when the drive roller stops. Since the film strip will still tend to waver, it is possible that the strip, when constrained against transverse movement by the drive roller and by the respective pins located at the gates, will waver while passing over the detector. The wavering could be to such an extent that locators for some frames will not be detected by the detector, thereby adversely affecting the operation of the printer.